In a temperature detecting apparatus including a thermistor, it is preferable to supply regulated power to the thermistor. However, the output voltage of a regulator that supplies power to the thermistor normally varies, and the impact of such variation on the thermistor varies with temperature. This means that the accuracy of temperature measurement varies depending on the temperature range.
Accordingly, Patent Literature (PTL) 1 proposes a technique in which to achieve accurate temperature detection in a wide range of temperatures, resistors are connected to both ends of a thermistor and switched from one to the other in accordance with the level (Hi or Lo) of a pulse signal. A voltage divided into two types, one for the high temperature side and the other for the low temperature, can thus be output from the thermistor.
Patent Literature 2 proposes a technique in which, in a temperature detecting circuit including a thermistor and a voltage-dividing resistor connected in series thereto, a temperature detecting unit is connected to a node between a temperature sensor and the voltage-dividing resistor and a series circuit of a resistor and a switch is connected in parallel to the thermistor or the voltage-dividing resistor. Patent Literature 3 proposes a temperature measuring apparatus that includes a series circuit composed of a thermistor and a main reference resistor, and an auxiliary reference resistor connected in parallel to the main reference resistor with a switching element interposed therebetween.
A memory means included in the temperature measuring apparatus disclosed in Patent Literature 3 has first and second temperature tables that contain data for low and high temperatures. In accordance with the output voltage of the thermistor, the first and second temperature tables are switched and the switching element is turned on or off.